1. Field of the Invention
The present invention relates to a sheet feeding apparatus usable in image forming systems such as electrophotographic copying machines, microfilm instruments, facsimiles, laser-beam printers, ink-jet printers and so on. Particularly, the present invention provides a sheet feeding apparatus which can effectively return a moving sheet from its position out of the path to its position in line with the path and also which can feed the sheet under its stable condition without flexure.
The sheet feeding apparatus according to the present invention is adaptable not only to copy paper, photosensitive paper and the like, but also to a resinous sheet as used in an overhead type projector, for example. Furthermore, it may be applied to original documents or punch cards.
2. Description of the Prior Art
The prior art will now be described in connection with a sheet feeding apparatus which can manually feed sheets one at a time by the use of slantingly arranged feed rollers, for example, in an electrophotographic copying machine.
As shown in FIG. 1A, such a type of sheet feeding apparatus comprises a slantingly arranged feed roller R, a guide G (transfer sheet side constraint) for transfer sheets to be manually inserted and a detection lever L for discriminating the presence or absence of a transfer sheet. When a transfer sheet P is manually moved to the detection lever L, a holding-down roller (not shown) is moved downwardly toward the transfer sheet P. Thus, the transfer sheet P is conveyed while being held by the holding-down roller and the slantingly arranged feed roller R. The conveying force is considered to be a vector T in FIG. 1A. If there is an angle .theta. between the roller R and the direction of the moving sheet P, the transfer sheet P will be subjected to a force Tsin.theta. which acts to urge it against the guide G. If the transfer sheet P is relatively thin or very wet, and therefore less rigid, it will engage the guide G due to the force Tsin.theta. to produce a flexure and/or corrugation or wrinkle in the transfer sheet (FIG. 1B). After the transfer sheet has been fed to the transfer station under the above condition, the transfer of the image may be partly void, or the transfer sheet may be wrinkled so that the image may be reduced in quality. On the contrary, if the force T is set at less value to prevent such a flexure thicker paper or curled paper can not be fed in good order. The force Tsin.theta. may be decreased if the above angle .theta. is reduced. In this case, however, the slanted feed of the transfer sheet will not properly be corrected. As will be understood from the foregoing, there is an opposing interrelation between the proper function and/or conveying force of the slantingly arranged roller and the flexure in the transfer sheet. It is desired that the transfer sheet can be fed without any flexure while maintaining the proper correcting function and conveying force.